The invention relates to a sensor element having a sensor surface forming part of a capacitive touch switch, the sensor surface being applied to the underside of a control surface. A preferred application is a touch switch for domestic appliances, such as e.g. cooking surfaces.
Sensor elements with a sensor surface forming part of a capacitive touch switch, in which the sensor surface is applied to the underside of a control surface, are known from the prior art. For optical function display purposes in the case of such a sensor surface or touch switch, in some cases in addition to the sensor surface LEDs or similar lighting means are fitted below the control surface. The problem then often exists that said lighting means light up a larger area than is desired.
The problem of the invention is to provide a sensor element of the aforementioned type, where an illuminated identification of a sensor surface is possible, whilst there is no undesired radiation of the lighting.
This problem is solved by a sensor element having a sensor surface, the sensor surface being a part of a capacitive touch switch. The sensor surface is fitted to the underside of a control surface of the capacitive touch switch. The sensor surface is at least partly light-transmitting and is illuminated from below by a light source. A light guide structure for a flux of light from the light source to the sensor surface is provided. The light guide structure shields the light source from the environment and from a remaining underside of the control surface. Advantageous developments of the invention are explained In greater detail hereinafter. By express reference the wording of the claims is made into part of the content of the description.
As a result of the light transmission of the sensor surface according to the invention and which can be in the form of transparency or translucency, in a simple manner a luminous marking can be produced in the vicinity of the sensor surface. Said luminous marking is produced by the light source fitted below the sensor surface. The light conducting or guide means ensure a reliable and essentially precise illumination of the desired point, namely the sensor surface or within the sensor surface. In this way the scattering of light outside the intended area is avoided, because it is prevented by the light guide means.
Advantageously there is one light source or one light guide means per sensor element. This permits an individual, optical identification of each sensor element. In the case of an arrangement with several sensor elements, this should be provided for each sensor element associated with an individual function. Generally used sensor elements can be provided with a common lighting means.
The light guide means are able to shield the light source touch switch against the environment, for example, against the entire environment below the control surface. In the case of a touch switch for a hotplate, the control surface can be the cooking surface, which can be made from glass ceramic material. Advantageously the light guide means shield the light source against other touch switches and/or the remaining underside of the control surface, which can In particular be light transmitting. Therefore a shielding action is particularly important with a light-transmitting control surface.
The light guide means can have a wall, which surrounds the at least one light source and forms a channel to the sensor surface. In this way, advantageously a closed channel can be formed between the light source and the sensor surface and is essentially closed in light-proof manner. The light guide means can at least partly be constructed themselves as a channel wall or merely comprise a channel or its wall. It is possible that they press the intrinsically loose sensor surface against the underside of the control surface and said pressing can take place elastically. Such a sensor surface can be constructed as an electrically conductive disk or platelet. ln particularly preferred manner the light guide means are made from plastic or are constructed flexibly. This simplifies manufacture and permits universal use.
The light guide means can form an electrical contacting means on the sensor surface, for example, of the associated sensor surface control. This economizes on separate contacting means, such as for example, cables or the like. To this end the light guide means are constructed in electrically conductive manner, such as electrically conductive plastic.
The light guide means can have a reflecting surface. If this is provided on the surface facing the light source, efficiency can be increased. This is particularly advantageous with light guide means in channel form, an inner aluminizing or silvering of the channel increasing efficiency.
In the case of the above-described sensor element, the light source can be variable as a function of the switching state of the touch switch. For example, it can be activated or deactivated in accordance with the touch switch and therefore optically indicate the switching state thereof.
So that the arrangement can be made as simple as possible, a light source can be arranged essentially below the sensor surface and can be coupled to the latter as the light guide means by means of a channel or the like. For example, the light source and light guide means can be placed on a plate below the control surface.
For displaying symbols or the like in the illuminated state, the sensor surface can be at least partly light-transmitting or transparent or translucent. According to one possibility it contains corresponding light-transmitting recesses in the form of symbols, which are to be displayed. The latter are transilluminated by the light and are displayed through the control surface.
It is also possible for the light guide means to guide or conduct light from the light source in the form of a symbol to be displayed onto the sensor surface. For this purpose a corresponding pattern or the like can be present in the light guide means. The relayed light is projected onto the sensor surface and brings about the display of the symbol and for this purpose the sensor surface is made light-transmitting.
Alternatively to simply constructed light guide means in a very short channel form, they can be constructed as plastic light guides. For this purpose a central arrangement of several light sources for different sensor surfaces is possible. The light can be guided to the corresponding sensor surface by means of the light guide means from said light sources. Such a central or concentrated arrangement of light sources can offer many advantages, including with regards to the simpler construction of the printed circuit boards.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is hereby claimed. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder.